Zinnhardt, B. | bioRxiv Science

bioRxiv2024

Imaging synaptic density in ageing and Alzheimer's Disease with -SynVesT-1

Monitoring synaptic injury in neurodegenerative diseases may provide new insights into the evolution of the degenerative process as well as a potential mechanism to target for preservation of function. Synaptic density imaging with PET is a relatively new approach to this issue. However, there are remaining questions about technical approaches to data analysis including reference region selection, and how specific phenotypic presentations and symptoms of Alzheimers Disease (AD) are reflected in alterations in synaptic density. MethodsUsing an SV2A PET ligand radiolabeled with the 18F isotope ([18F]-SynVesT-1) we performed sensitivity analyses to determine the optimal reference tissue modelling approach to derive whole brain ratio images. Using these whole brain images from a sample of young adults, older adults, and patients with varied phenotypic presentations of AD we then contrast regional SV2A density and in vivo AD biomarkers. ResultReference tissue optimisation concluded that a cerebellar grey matter reference region is best for deriving whole brain ratio images. Using these whole brain ratio images, we find a strong inverse association between [18F]-SynVesT-1 PET uptake and amyloid beta and tau PET deposition. Finally, we find that individuals with lower temporal grey matter volume but higher temporal [18F]-SynVesT-1 PET uptake show preserved performance on the MMSE. Conclusions[18F]-SynVesT-1 PET shows a close association with in vivo AD pathology and preserved SV2A density may be a possible marker for resilience to neurodegeneration.

neuroscience↗

bioRxiv2024

Characterization of AZ12464237 as a high affinity, non-nucleotide antagonist radioligand for the P2Y12 receptor

The purinergic receptor P2Y12 (P2Y12R) is a well-recognized target for anti-thrombotic agents. This receptor is also expressed in microglia, where it plays a key role in neuroinflammation and microglia activation. To investigate P2Y12R-mediated actions in the central nervous system (CNS), the development of novel brain-penetrant ligands is essential, along with further in vitro studies. A radiolabeled, easily accessible tool compound would significantly advance such drug discovery efforts. Herein, we describe the 3H-labeling of a non-nucleotide P2Y12R antagonist AZ12464237, and its in vitro binding properties to the receptor in membrane preparations form transfected cells, as well as on mouse brain tissues. The radioligand shows high affinity toward both the human and rat P2Y12R in transfected cells, with Kd values of 3.12 {+/-} 0.70 nM (human) and 16.6 {+/-} 3.4 nM (rat), as determined by saturation binding studies. The binding kinetics of [3H]AZ12464237 are rapid with a short target residence time ([~]1 min). We further confirmed the selectivity of the radioligand by performing competitive displacement studies, in which reported P2Y12R ligands and other P2Y receptors ligands were tested for binding against [3H]AZ12464237. Additionally, the radioligand proved useful for in vitro autoradiography studies on mouse brain tissues, although a small amount of off-target binding was observed in P2Y12R knock-out mice. This could be traced to glycogen synthase kinase 3 . Considering the growing interest in P2Y12R as a biomarker for microglia activation, [3H]AZ12464237 represents a promising tool for in vitro studies, including screening assays aimed at identifying novel P2Y12R ligands for CNS applications.

pharmacology and toxicology↗